Duplex high-frequency telephone system



May 6, 1930.

DUPLEX HIGH FREQUENCY TELEPHONE SYSTEM Filed Dec; 23, 192 5 2 Sheets-Sheet l glwvento'a R. D. DUNCAN, JR 1,757,114 J y 1930- I R. D. DUNCAN, JR 1,757,114

DUPLEX HIGH FREQUENCY TELERHONE SYSTEM Filed Dec. 25, 1925 2 .Sheets-She t 2 upon the zlocal receiverisystem.

Patented May 6, 1930 s me 0 ,mse cite. essence I I .sxsl em reunifica io em mew 1 5: sme in- 7 299:

My invention relates 'broa dly ito electricel signaling and more .perticnla' xily to a duplex high frequency itelephone communication system. 1

' One of the objects "of :my inventionis .to proyide .a practical circuit arrangement for the simultaneous operation of fsignaltransmission and reception apparatus in e communicetion system atgtheisameZterminelwithout 'interfei'ence of. the" .transniittingxenergy f Another object. of my 2in1vention isto pliQf vIicle apolyph-ase system of radio telephone ,communic'ati, n wherehigh frequency signaling energy is impressed upon the ,utilization circuit such es a llne wlresystemcr ;1 radio antenna, which also connects with the .re'cei v; ing system for the simultaneous transmission .encl reception ofmodulated high fre quency current, where the currents in one of r the phases of theitrensmitting systemere employed'to' eliminate currents introduced into r the receiving circnitbyithe localtransmitte All forpreventing@locelinterference. 7

Still another obj eat of my inven ion i 1 0 provide athree phasehigh 'freguendy current iIIQIL IHLSSIOIIfiyst lllfipfi fltlng An e a redla ing system orflcerrier wave line wiresystem with a receiving apparatus connected in the same isystenrfor simultaneous op rfil ioll Q1 frequency closely related :to the ransmi n frequ ncy, withmeansin th neceiying epp l'atus for deriving energy from onei o f the phasesof the ti a'nsmissi n yst m tor-mu teracting the local efiects of the transmitter upon-the receiver.- e

7 A further object ,of nyint'en'tion to vide a duplex adi t lephone system in i ihlfih simultaneou mone QQmmll lleg t on may b conduc edflnethe same-ant nna w thmitintee clue tot ezlecel a sm tter HeRetOfQEe -inthe art,duple c;systemfi,qf. iar die telephqny elm-the same :61: en loses centantennze ha-ize been.nelatively-complicet:

ferenc from .sidetalkin'theteeei nelsystem ecl and'have depended lergelyglpqn'f fidge or balanced circuitszin which the efieetioiithe transmitting circuit :is neutrehzecl .YQI ;-ba=lnormal frequency trensmittergind t the A I extreme 's'ensitiyity of the receiving equipment Without such balancing circuits, 'eYen With the transmitting and receivingf frequen cies fairly Widely-separated, thein'tense magnetlc and static fields established by-the transmitting current tend to paralyze'thereceiving apparatus; end render it practicallyfimpossible .ato simultaneously @trensmit and re-7 celve on .thesame oron closely edjacentlani 'tennee,

present invention I providea t hree phaseh ghsfrequency genereting system with connections for impressing "a portion of the high frequency energy upon a utilization cirin a-three ph se; system, :the high frequency energy which is arbitrarily introduced into the receiving system from the transmitting systemihas itstime'phase in directoppositio'n to :the time phase of the energy existing in thefreceiving. circuit by action. from thegtranf mitting circuit'alse result of whichinterfen ing. currentsin'rthe receiving systemare neu- 'virtue, ef'thepe'cu-lier phase relations existing tralizled end the ineceiving circuit ,:func,ti0ns Y 'xyithcutinterference from thelocziltmnsmitting system; :In this manner sininlteneoufi tiitilSiIlISSlDIi a'nda recept on r en the .sz me enbe ccnducted without mechanical .switchiiig means between ;t etmns n ttingend recei-vset-pa ents- 'flnemy fLetfeliS :Betent :1 $811,025, ated July e iezeimethed wf 1 dicte ep ten iis trensmis 'QIn enelreceptioi r-ecei 'ngeenitennae ereesepereteibil e escleeeiaieentfi he method beingbesedpn the pecu1-i-ar', phes ew le kinsa x' phase z lbQdQ wherein 451153 a iiensm tting and 2 etenna or.theesametwireiutilizetion iciicui em'ey I :Figure ,1 shows ductance 'a single antenna; Fig.

duplex high frequency telephony and employs three phase high frequency current for transmission but discloses circuit arrangements wherein the same antenna isemployed for transmission and reception, which feature is ofextreme advantage where space for the erection ofantennae is restricted such as on shipboard or on aircraft. The present system, is also applicable to carrier current or wired radio operatlon over a line wire system,such as a pair of telephone wires or conductors for an electric power distribution system where in effect the transmittingand re ceiving antennae are one and the same by vir tue of the inherent constructions of the system. .1 1. The difiiculties of obtaining a satisfactory duplex high frequency telephone system with the sameior with closely-adjacent transmittingand receivingantennae, as herein set forth, are all overcome by thepresent invention;

My invention will be more fully understood from the specification hereinafter following by reference to the accompanying' drawings, wherein fundamentalsystem of connection according to my invention for space radio operation on 2 is a modification of Fig. 1 showing the adaptation of myinvention to a carrier wave line wire system Fig. 3 shows 'thecomplete circuit connections for a duplex space radio system ,and Figs. 4, agb, 0, are Vector diagrams of the difierent currents, voltages'and magnetic fluxes that are established in the transmitting and receiving circuits of the system of my invention."

Referring to Fig. '1,the numeral 1 represents a source. of three phase highfrequency current assumedto be modulated by the voice or otherwise by methods not shownand not hereessentiah Source 1 operatesinto three Y connected primary inductances (A connect-ion maybe employed), 2, 3, 4 of transformers 5, '6 Inductively coupled to pri'-' mary inductances 2, 3, areurespectively, secondary inductances 8, 9, whlch are connected in series with each otherand with the antenna 11,:parallel tuned circuit '12, and-ground 13;

Connected between points AB, i. e.,' in parallel-with circuit 12, inductances 8 and 9,"is series circuit composed of parallel tuned circuit 14, andi-nductances 15,16. Circuits 12 and 14 respectively, arecomposed of induc tance 17, capacity 18, and inductance 19,,capacity 20. Inductively coupled Within'ductance 15 is receiving circuit 21, and electron tube detector 22, containing telephone l re ceivers 23 in its plate circuit; Inductively coupled to primary inductance 4, andto in- 16is circuit-24 made up ofinductances 10 'and -25, variable capacity 26 and variableresistance 27 Circuits 19, 21 and 24 are shown to be shielded by metallic shielding diagrammatically the up of inductance29,and capacity 30;

The circuits shown in Fig. 2 are similarto those of Fig. 1, with the exception that antenna 11- is replaced by carrier wave transmission lines 31 which are connected with points AB through capacities 32, 33. V p

"In Fig. 3 I have shown acomplete radio transmitting and irece1ving""system embodying the principles of myinvention, in which an electron "tube? generator; of. the kind more particularly de- "scribedin myco-pending application Serial No. 61,019, filed October 7,1925, and my Letters Patent-1,578,881, dated March 30,1926.

three phase high frequency,

Reference is madeto the saidco-pendingapplications for a complete description ofth e' three phase highfrequency current generator. For the purpose of explaining the operationof theduplex system of the present applicationzit will be sufficientto observe that a single phase high frequency current generator of any suitable type,.illustrated here by reference character electron tube type, isfconnected as illustrated by reference character 40' to the tuned -sy's-' tem 39 which is coupled throughtheY connected inductancevsystem 37 with. electron tube high frequency'fpower amplifiers 34, 35 and 36, the output' circuits of which impress polyphase high frequency signaling energyv on the transmitting antenna? system 11,- through coupling coils 2 -58 and'3 9. Ena

ergy deliveredffrom amplifier 'circuit 36 is impressed upon the link circuit 24 through coupling coils 4 10, and is in turn impressed upon the receiving system'through coupling coils'2516.- Modulation of the'system is secured through parallel connected tubes 43," 44 and '45, controlled from microphone 42, connected in the input circuit of the amplifier. The receiving'system is coupled to'the antenna circuit through inductances 15 -21, as described in connection with Fig.1. The'operation of circuits of Figs. 1 is 'as-f'ollowsi 1 1 'Referring to Fig. .4and Fig; 1, three phase high frequency currents' ii, 21 ,2}, are gener- 90 41 as of the self-excited less and 2 ated by three phase source 1 and havethe relationship represented in vector diagram c ef Fig. 4 where they are displaced'in time phase by The vectors are, in accordance with conventi0n,lassumedto rotate in a counter} clockwise direction. Current 6 establishes magnetic field (p shown vectorially in Fig. 4 in time phase with i -and'which links induct-ances 2 and 8 as indicated by a dotted line in Fig. 1. Magnetic field (p induces a drivingvoltage e in inductance '8. lagging in-phase'as shown in Fig. 4 by 90; The same is true with'magnetic'field (p linking. inductances 3, and 9, as shown in dotted lines in Fig.v1,;pi oduced by current 71 which in-j V V circuit- 14, and inductances 1'5 ducesa second driving-voltage a in induc tan-ce'8rand lagging behind the magnetic vector by 90 121 s" shown in F igQ 4 I In :anormal balanced systemiz' =fi ',x =l o andhence e =:e The resultant driving voltageaexlstent :in the transmitting branch of the antenna circuit-is,the-vectorsum o'f e and e 5 or cTi, shown iii-Fig. 4?, which due tothe 120 phase relation is equal 1 in amplitude to "611 or c and lags the former or leads the latterwhy 60!) Nowithezantenna circuit 11, composed of the inherent antenna inductance and ca pacity 29 and:30 together =w i-th-icircuit' l 2, and

inductanCesS and 9,-iszadjustecluto'be in reso nance with the transmitting frequency fi of source 51, and hence the transmitting curr-en't quency 7 which is .d -ifieren't fremthe tra ns- I mittiaig. frequency 7?}.

is greater than t circuit 12 will have the properties of an" inductance at frequency lf if f is less than circuit 12 will ibehaveas capacity at ire quency 7%. In eitherenent circuit will lead the transmitting curl-e *t 1% since for eflicient inductances" 8", 9, will he 10-win comparison with their reac-tancee. Now Voltage e is impressed branch of the antenna circuit composed or unless bala-ncedout prod-11cc interference in the "local receivinecircu-i-t 217-22; Circuit 14 made up of parallel connected inductance 19" and capacity 29 isadjnstecl'fer "reeonance at- I the transmitting frequency H offer a very high impedance (infinitely high 7%, andfhence will in the ideal Casey-at this h'equencyi llnder this condition the inaj or portion of the trans l q mitting current 1} -will pass into the elevated portion 1110f the antenna and be a-ra ilaliile for radiatingsignals; only a fraction of the c.ur-. rent Will'be diverted from thehh'tnnhI hack to the-ground connection 13, throughthe I receiving 'b'ranchl4, 15, 16, j Experience has shown t-hat however-perfect it is practically possible to make the rejecting properties .of pam l lel tuned circnit'14, with relatively" high transmit-ting powers and sensiti vi ties got I the local receiving circuits, .the small frat '0 the local receiver and with the proper adjustment of induc -tance 17, 'and capacity 1 8' hy an angle B, '4 shown in Fig. -4 -to be slightly less than 90,

nmgy be made equal in amp operation the resistances of directly 7 across "the: --receiving,

and 16. and" will,

. offer an exceedingly pessibleierten with Widely separatedwalnes ot andflO as s'hown inidottedlinexinFig; 1, .Mag rnetlcifield zi induces a drawing yoltage 6 5m 1nductance 10 01f circuiti-24 as shown in'Fig."

4 lagging (p3 b-y'QO ireuit24virtue of adj ustinents of inductances 40325,;21116wax-1- able capacity and'resistance26arid'27,is pref erably adjusted to b light-1y ofBresonanem here showni" I the current established hy o'lt'age jc "legs 6 *by anangle 19;as shown in Fig. 4. Current it establishes" a rna-gnet-ic field with 2' and which links" inductances 25 and 16 as shown inclottec'l' lin'esin Fig. 1. Mag:

ne'ti'c field induces driving voltage 8 in 'lnductan cell'fi lagg1ng1p' -g I in Fig. 4?. "The amplitude offe g is var able and determined by the intensity of'jcur rent i the c egatee of coupling at inductances 4,' 10 and lfi, 25, and variable resistance 27;

tive direction, so that in phase I as shown V I-twill be' noted that thevdltage e sub! stantia lly coincides in phase with en; a (180 reversalin phase mey thereforebe obtained v by hav ing'the couplin s at 'indnctanc'ejs 4- -1O respect to each and 16+25 reversed other, "in which condition the balancing 5 neutral'izing -Voltage Fee gis obtained which is substantiallyfopposite I h ase to 653 {an d Etude therewith.

ion

Interfering-currents the receiv 'cbrai-ich I of the antenna maythereforebefec inpleteh balanced out. l he shielding"of-currents 14,,

-1- 'and 94h as 7 been t'ui-idi preferahle es- {el ec tric fieldsiaretherehy'prevented froi T ac'tii-ig" upon the circuits soshlelded-an d a more co'mplete balancing out otinterferenee obtained The 1 eceiv1ng Wa e ot-frequency 1mpinging-upon theelevatedportion o the an? tennawill iestabl'ish current-s t herei-nlo t tlirat frequency; iwe paths are presented for the passage act these currents, the transmission branch 12, 8, 9; and the receivingfbrlanch 14, j

15 '1 6; No-w g'the complete receiving antenna circuit 29,330,144, 15, 16-is tuned to resena-nce for frequencyf and hence offers a louf impedance to em rent-s of this frequency Paralte l tuned 'c'irc i for receiving rents of fr que cy f Q The-r portion ofthefirecei-Vin'g cu rent; will flew threu'gfl'i thereceiving'hranchf '4', I6 and I I n afiect in't'h '--desir ed inamierjthe receiver ci-rot the t-ransmlttlng currentwhiclrfiowsfhack to the ground through the recei-ving'hranc h is 12is adjusted te nesona-nce I I .reqrreney f and hence the transmission branch containing circuit I2 will high inipeda'n ceflto cirri fore, the min" as he mamas and: circuits 511a ain't-ea I maybe conducted with 'sufitabIe transmitting to excessive? and disturbing; side tones.

and receiving frequencies without either complete paralyzing of the local receiving apparatus by the local transmitter or giving riIse n fact,the absence ofside tones may be so complete, that the operator will 7 be unable to hear any of his own conversation,which for many reasons is often an undesirable COIldls tion so'that the balance obtained at link circuit 24f may be arbitrarily disturbed so as to yield side tones of the required intensity.

I have illustrated only one method of mod- Y ulation whichmay be employed in'the trans- I tector illustrated here1n,'or-'lvar1ous arrangemitting system, butit will be understood that grid modulation oroth'er' arrangements, of circuits may be provided for effecting the transmission of signals. It will also, be understood that I may employ other'arran-gements, of detector circuits and that a crystal detector may be used in lieu of the tube dements of amplification systems may be pro vi'ded at the receiver for reproducing the de sired signals. f I j I The completefi'eeclom from disturbing side tones-is brought about by the doublybranched antenna circuit and'the introduction .of a neutralizing voltage into the receiv ing branch-for obtaining duplex operation.

The phase relations of the currents in the system described herein as distinctfrom other systems employin-gadouble branched anten. na'and a neutralizing voltage obtained by elaborate phase clisplac'ingcircuits", are automatically fixed by the three phase 'source and the system accordingly lends itself to l I wards extreme simplicity and stability in op-- eration. The variable features of the link circuit and'the circuits 12 and 14 permit ad-j justmen-ts to be made inorder to adjust for departures from more or less ideal conditions in the system.

While Ihave described'jmy invention in certain particular embodiments I desire that r it be understood. that modifications may be made and that no limitations upon the inven tion are intended other than are imposed by the scope of the appendediclaims.

lVhat I claim as new and desire to secure by Letters Patent of the United States is as followsz fl f y r 1. In a simultaneoustransmission and re ception system of radio telephony," the combination of an antenna-ground system, 'two branchcircuits connected in -parallel, one of said branch circuits containing a parallel; tuned circuit, said parallel connected branch circuits connected in series with said antennaground system,v a signal receiving system,

said signal receiving systemlconnected with said branch circuit containing saidparallel tuned circuit, a source of three phase highfrequen cy electrical energy, said second branch circuit connected "with two. phases offsaid s e. le eeears areresa h ei eet-r of one of said branch circuits adjusted substantially' to resonance for the frequency of said three phase source, a linking circuit con-- nected with the third remaining phaseof said three phase source and with said branch cirsource and interconnected in a three phasemanner, a single antenna system, alpair of branch circuits disposedin parallel with said antenna system, saidfcircuits containing; a plurality of'inductances, two i of said in ductances'being inductively coupled with. two

of said first' mentioned inductances, a signaltranslating and responsive means associated with oneof the inductancesin said antenna system, a link circuitcontaining at least two inductances in series connect1on,-one of said link circuit inductances inductively coupled to the remaining 10f; said three first mentioned. inductances, the remaining of said link circuit inductances inductively coupled. with another inductance adjacent said signal translating and responsive means, said link circuit being adjusted to establish in said signal translating and responsive means a current for neutralizing the effects of said source, 1 r

;3. :A radio telephone transmitting and receivingsystem comprising in combination a transmitting system, having a source of three phase high frequency current, a plurality of electron tube circuits corresponding in' number to-the number of phases of said source, an input circuit foijeach ofsaid electron .tube circuits, in-V ductances in each. of said input circuits electricallyassociated witheach pha'seof saidthree phasesource, an'output circuit for each of said electron tube circuits, said output cir-' cuits each containing. an inductance, an antenna system, a pair of branch circuits disposed in parallel' with said antenna system,-

one of said circuitsbeing inductively coupled to two of said output inductances, independent inductances in said antenna system; means for. effecting telephonic modulation of the'high frequency energy existent in said electron tube circuits, .a signaltranslating and responsive means electrically associated with one of said independent inductances,a link circuit containing a plurality of inductances, said link circuit inductively coupled tothe thirdof said output ,inductances of said-electron tube circuitsand to another of said independent inductances, the adj ustment oi -said transmitting and receiving antenna systems and of said link circuit by virtue of the opposing phase relations of the voltages established in said antenna system by the current in said transmitting system.

4. A system comprising in combination a common antenna system, a pair of branch circuits connected in parallel thereto, a source of unmodulated three phase electrical energy, means for impressing energy from two phases of said three phase source upon one'of said branch circuits, means for impressing energy 7 said antenna systems for effecting telephonic V modulation of said three phase high" fre quency electrical energy.

ROBERT D. DUNCAN, JR;

radio telephone communication 

